Recently, social anxiety caused by the frequency of terrible crimes is increasing. Then, surveillance cameras have been introducing to be equipped in a busy place, where person haunts in shops, companies or the like, in order to supervise suspicious person by picture images. This system is designed to be equipped with the surveillance cameras in a shop or an entrance as a surveillance spot to monitor image transmitted from the surveillance cameras in a monitor room and to record the image.
In such a supervising system for image, there is a possibility that suspicious person may narrow a range of vision for supervising and commit a crime by obstructing the surveillance camera with a cover, spraying the surveillance camera, or changing a direction of the surveillance camera. While a supervisor may notice a dishonest practice (a scheming behavior) by monitoring the view, the dishonest practice cannot be recorded in the surveillance camera, in a case where only the recording of image is practiced by a surveillance camera.
Then, a system for detecting an obstruction against a camera, that is, a scheme in accordance with an image taken pictures by the camera and a value obtained by an illuminance sensor has been known. Japanese patent laid-open publication No. 218,189 of 2001 may be referred to as an example.
This system is designed to judge whether a scheme exists or not in accordance with a luminance value of an image as taken pictures and a value of illuminance sensor measuring a supervising area. In a case where the luminance value of image as taken pictures is out of the prescribed value and the illuminance value is the prescribed value or more, it is judged that the above scheme has occurred, as the image taken pictures, that is, an area surrounding the camera lens is considered to be abnormal and the supervising area is considered to be normal.